Long-lived, sturdy herbaceous peonies lack yellow flower colouration in their palate. Breeders long attempted in vain to achieve yellow-flowering peonies on plants with the desirable garden qualities of herbaceous peonies by crossing tree peonies, which do produce yellow flowers, with herbaceous peonies. Success finally came posthumously to Japanese gardener Toichi Itoh in the early 1960s when several of his seedlings from crosses made 16 years earlier bloomed with richly coloured, double yellow flowers.
After some 20,000 crosses, in 1948 Toichi Itoh succeeded in crossing the yellow tree peony Alice Harding with the white-flowered herbaceous peony Kakoden, resulting in the first blooming intersectional hybrids in the early 1960s. Several of the plants produced deep yellow double flowers. Louis Smirnow, an American horticulturist, received permission from Itoh's widow to patent some of the plants in the late 1960s. Yellow Crown, Yellow Dream, Yellow Emperor and Yellow Heaven were brought to the United States in the late 1960s and registered in 1974. Some experts believe that these currently marketed Itoh peonies have been confused over the years. Toichi Itoh died in 1956.
While the foliage of intersectional peonies is similar to that of tree peonies, their habit and cultural requirements are closer to that of herbaceous peonies, though requiring somewhat less winter chill. Plant and care for intersectional peonies as you would herbaceous peonies, except plant the roots of intersectional peonies 1 inch deeper than those of herbaceous peonies. Prepare the planting site well ahead of planting roots in the fall. A large hole dug 2 feet deep and wide and filled with good garden soil mixed with organic compost provides a permanent home for the long-lived plants. The buds for the following season's flowers are produced in the autumn.
Yellow Intersectional Peonies
Breeders have developed outstanding new yellow hybrids in the last decades of the 20th century in addition to the yellow intersectional peonies bred by Itoh. Border Charm, Prairie Charm and Garden Treasure bred by Don Hollingsworth have proved to be worthy plants. Garden Treasure, a plant of exceptional vigour and beauty and large, pure yellow flowers, won the Gold Medal of the American Peony Society. Roger Anderson introduced Bartzella in 1986, considered the current standard for yellow intersectional peony flowers and plants. Especially desirable varieties are in demand beyond supply, fetching up to hundreds of dollars for a single root.
Other Colors of Intersectional Peonies
Roger Anderson's intersectional hybrids include Kopper Kettle, introduced in 1999, a blend of apricot, yellows, pinks and red, giving the impression of copper colouring. Cora Louise is white with dark lavender flares. Anderson's first introduction, First Arrival is pink with lavender shading on an attractive plant. Julia Rose opens cherry-red, eventually fading to orange-red, then yellow, with all colours often showing at once on the blooming plant. Scarlet Heaven flowers in brilliant scarlet single flowers. Hillary is double to semi-double flowering in medium pink.
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- University of California; Sonoma County Master Gardeners; Peonies
- Paeonia Newsletter; Intersectional Hybrids
- Horticulture -- The Art and Science of Smart Gardening; Improbable Peonies; James W. Waddick; March 2003
- Cornell Cooperative Extension -- Suffolk County: The Culture of Herbaceous and Tree Peonies; Thomas Kowalsick; November 2008
- "Sunset Western Garden Book"; Kathleen Norris Brenzel, et al.; 2007